Try hormones. We had a racehorse who was bought as a colt. We have a farm filled with mares and only 3 pastures. We had to geld him. He lost his "edge" in the race so the vet perscribed us hormones. We were suppose to give him 1cc and we end up giving him only half that and there is a change. He doesnt act studish but he does have more of an edge to him. Have to talk to her vet about some ideas that may help.
A Dog looks up to a man,
A cat looks down on a man,
But a patient horse looks a man in the eye and sees him as an equal